It depends a little on how you're using your metronome to practice. My instructor once guided me to turn the metronome down to a speed where I was confident that I could play the piece 100% with no mistakes. When first learning a tune, this could be painfully slow. Each subsequent time I would sit down to practice this piece, I would start again at this tempo. After a couple of run throughs at this speed, I would increase the metronome by 10 BPM, after a couple more run throughs, another 10 BPM increase, until I was one or two "clicks" (increments of 10 BPMs) above the desired speed of the song.
After I played it a few times at a speed faster than the destination tempo, I would turn the metronome back down to the desired speed, and suddenly my technical accuracy would improve, since I started from 100% accuracy, and built up slowly to a tempo above the destination tempo.
I agree with another poster here that getting bored with the tune is actually a good thing. You want to be as comfortable as possible while playing the piece, not frantic in a "hanging on for dear life" mentality while playing the piece. It should seem effortless, not really difficult during the performance. Stepping up the BPM slowly should help in this effort.